Abstract The long-term goal of this project is to determine the role of the perineuronal net (PNN) and its glycosylation in Alzheimer's Disease (AD) in response to one of the High-Priority Research Topics for PAR-18-596, namely ?Deciphering the Glycosylation Code of Alzheimer's Disease?. Glycomics (glycosylation or sugar codes) are the third molecular language of cells. Recent data suggest that glycosylation pathways play a role in AD and have emerged as an area of research for understanding and developing treatments of AD. For example, many key proteins associated with AD are glycosylated, including amyloid precursor protein, BACE1, neprilysin (NEP) and triggering receptor expressed in myeloid cells. PNN is a lace-like cloak of ECM enwraping primarily a selective class of fast-spiking inhibitory interneurons expressing calcium binding protein parvalbumin (PV). The PNN is primarily comprised of members of the lectican family of chondroitin sulfate proteoglycans (CSPGs), hyaluronan, tenascins and link proteins. The CSPGs are an array of core proteins attached with varying lengths of CS, which is a glycosaminoglycan composed of disaccharide units formed by glucurionic acid (GlcA) and N-acetylgalactosamine (GalNAc). Several lines of evidence support that PNN plays a role in AD and may be a therapeutic target. First, PNN is significantly reduced in the AD brain. It has been postulated by Roger Tsien that very long-term memories may be stored in the pattern of holes in the PNN. Second, recent data demonstrate that PNN is exclusively associated with PV+ interneurons expressing metallopeptidases Adamts8, Adamts15 and NEP. NEP is one of the most potent A?-degrading enzymes. The impairment of neural network oscillations at different frequencies that mediate local and long-range communications for brain functions leads to cognitive and behavioral deficits in AD. These PV+ play essential roles in the generation of ?- frequency neural network oscillations. Optical activation of PV+ interneurons at ?-frequencies has been shown to attenuate amyloid load and improve cognitive function. Finally, GlcA and GalNAc at carbons C4, C6, and C2 may be sulfated in either combination and has profound effects on synaptic integrity and function. It has been reported that 4-sulfate chondroitin (C4S) inhibits axonal growth and neural plasticity while C6S promotes axon regeneration and neural plasticity. Moreover, C4S blocking antibodies have been explored to alleviate neuropathology in mouse overexpressing mutated Tau protein. Finally, preliminary results showed aberrant ?- oscillations associated with impairment of PNN and PV+ interneurons in AD mouse model line 41. Furthermore, viral-mediated over-expression of neuregulin1 (NRG1) ameliorates neuropathology and improves cognitive function in line 41 mice. Brain cholinergic neuron-specific NRG1 mutant mice display impaired PNN. Based on these results, Aim 1 is to characterize the PNN state of glycosylation during progression of AD. Aim 2 is to determine whether manipulation of PNN glycosylation modifies progression of AD. Aim 3 is to determine the role of NRG1 signaling in the formation and maintenance of the PNN.